I would say that one minute is not enough time for your pupil to become completely adjusted; however, doctors spending the necessary time (20 min. or so), ties up the exam room & puts other patients in the waiting room much longer.

Actually, though your eye may dilate a small amount more as you wait longer, it likely wouldn't be much more. At most, half a milimeter, probably less. Dark adaption is more than just a larger pupil size. Much of dark adaption is due to chemical changes in the vitrious fluid of the eye. This is what takes 20+ minutes to be completed.

Folks talk about this all of the time, but I never hear anyone question (except me) how accurate any such measurement can be given that the brightness of what we see is very dependent on the target as seen through the eyepiece, and so at any given moment who knows the amount of dilation?! For this reason, I think the whole endeavor of measuring one's dark adapted pupil and then using that number in any kind of actual observing context is bogus.

Folks talk about this all of the time, but I never hear anyone question (except me) how accurate any such measurement can be given that the brightness of what we see is very dependent on the target as seen through the eyepiece, and so at any given moment who knows the amount of dilation?! For this reason, I think the whole endeavor of measuring one's dark adapted pupil and then using that number in any kind of actual observing context is bogus.

I believe that the eye quickly dilates to essentially its maximum aperture and then the chemical processes that are the major part of dark adaptation begins.

The surface brightness of any extended object is proportional to the square of either the exit pupil or the eyes entrance pupil, whichever is smaller. If you eye is dilated to 6 mm and exit pupil is 6mm then it would 4 times as bright/intense as that same object viewed with a 3mm exit pupil.

I think you are missing my point? Some targets are brighter than others, and so one's pupil will adjust depending on the target. There is no one number that is valid for all targets. In fact, I think this fact accounts for why it takes time at the eyepiece to see a lot of detail in anything - one's "dark adaption" needs time to adapt to whatever is coming out of the eyepiece for that target.

Folks talk about this all of the time, but I never hear anyone question (except me) how accurate any such measurement can be given that the brightness of what we see is very dependent on the target as seen through the eyepiece, and so at any given moment who knows the amount of dilation?! For this reason, I think the whole endeavor of measuring one's dark adapted pupil and then using that number in any kind of actual observing context is bogus.

I strongly suspect that the Moon and Sun are the only astronomical targets bright enough to make your pupils contract.

Contrary to widespread lore, my measurements indicate that there's no difference in pupil size between full and moderate darkness, such as one would find on a typical suburban ball field at night. At least for me ... can't speak for other people.

I think you are missing my point? Some targets are brighter than others, and so one's pupil will adjust depending on the target. There is no one number that is valid for all targets. In fact, I think this fact accounts for why it takes time at the eyepiece to see a lot of detail in anything - one's "dark adaption" needs time to adapt to whatever is coming out of the eyepiece for that target.

Unless you are looking at objects with very high surface brightness with a very large scope, I think the pupil remains at its maximum size. I have noticed that dark adaptation can be affected briefly after viewing a bright object, but that's at the low level of the biochemical changes people have brought up in this thread.

A great way to measure pupil diameter (when you have no observing plans) is to wait a couple minutes in a completely darkened room, and then take a flash photo while you hold a ruler near your eyes. Then measure it from the photo. I got 7mm with a precision of better than 0.5mm last time I tried it. Note that an electronic flash this isn't the most pleasant thing to look at when you're dark adapted, but it won't kill you either.

I have to say that (I think) that my experiences out observing lead me to believe otherwise. When well dark adapted, certainly Jupiter and Saturn are painfully bright - seems to me more so than walking out of the optometrists without the disposable sun glasses. Looking at an unfiltered moon results in total blindness. Even my Quickfinder and Telrad have to be dimmed almost to extinction, and only newbies use a red light at anything other than the lowest possible level. A green laser beam is like a stick in the eye. Also, and as I said, I think that one reason why it takes time at the eyepiece to see faint/difficult stuff is that it takes some time for the eye to adjust to the field brightness. So, my guess is that there is a HUGE amount of mythology about entrance pupil size and dark adaption. Maybe or maybe not so much on faint fuzzies, but certainly on many targets that I think most folks would agree appear really, really bright through the eyepiece.

Our club has a dark sky meter, and the next time I observe at our site I am going to use it to check the brightness through the eyepiece when positioned on different targets. Good idea?!

BTW, I just read on Wikipedia that pupil dilation/contraction is also affected by **** attraction. I don't know about you old folks, but in my case that is still something that has to be factored in.

I have to say that (I think) that my experiences out observing lead me to believe otherwise. When well dark adapted, certainly Jupiter and Saturn are painfully bright - seems to me more so than walking out of the optometrists without the disposable sun glasses. Looking at an unfiltered moon results in total blindness. Even my Quickfinder and Telrad have to be dimmed almost to extinction, and only newbies use a red light at anything other than the lowest possible level. A green laser beam is like a stick in the eye. Also, and as I said, I think that one reason why it takes time at the eyepiece to see faint/difficult stuff is that it takes some time for the eye to adjust to the field brightness. So, my guess is that there is a HUGE amount of mythology about entrance pupil size and dark adaption. Maybe or maybe not so much on faint fuzzies, but certainly on many targets that I think most folks would agree appear really, really bright through the eyepiece.

Our club has a dark sky meter, and the next time I observe at our site I am going to use it to check the brightness through the eyepiece when positioned on different targets. Good idea?!

I discovered long ago, in any field or endeavour, given X number of people, you'll get X number of opinions....we're all different. For all our discussions, rants, and raves, bottom line is, only the eyeball to eyepiece will tell...

I have to say that (I think) that my experiences out observing lead me to believe otherwise. When well dark adapted, certainly Jupiter and Saturn are painfully bright - seems to me more so than walking out of the optometrists without the disposable sun glasses. Looking at an unfiltered moon results in total blindness

Your eyes entrance pupil is not relevant when viewing the planets and double stars because they are done at higher magnifications and small exit pupils. In any event, a dark adapted eye is not the best choice for viewing planets, adding some ambient light is one technique used by planetary observers to prevent dark adaptation.

The discussion here I believe is about observing deep sky objects were dark adaptation is critical. In this situation, the eye will be fully dilated regardless of the brightness of the DSO.

Bye the way, viewing the moon does not result in total blindness, it just results in losing ones dark adaptation. It's probably the only object bright enough and large enough to cause this loss. The contraction of the pupil when viewing the moon is the reason that one can often see the secondary's shadow at low magnifications.

A better way of determining if Tony's observation about pupil size applies to you would be to go out in a suburban setting in which you can barely see the Milky Way, and take the flash photo of your eyes with a ruler, as I recommended. Then close yourself in a dark room, and do the same thing. The darkest sites in the world are nowhere near the darkness of an indoor room, so you will be overestimating the difference. Then report your measurements here.

I asked my ophthalmologist this question about a year ago. I am 71. The answer was that my open iris measured about 4mm. I should point out that my iris has been affected by the use of eye constriction drops for many years, a necessity because of my glaucoma. The 4mm value was about what I had measured previously.

I have to say that (I think) that my experiences out observing lead me to believe otherwise. When well dark adapted, certainly Jupiter and Saturn are painfully bright.

Yes, the planets can appear painfully bright for a short time, at least through a big telescope. But that's due to the chemical changes, not the pupil size. It takes your pupil a measurable fraction of a minute to dilate fully, but it takes less than a second for them to contract.

Try it. Go into the bathroom at night, turn the light off, and wait for a minute. Stand in front of the mirror and flip the light on. You can actually see your pupils contract. It's even more obvious if you look at someone else's eyes.

A great way to measure pupil diameter (when you have no observing plans) is to wait a couple minutes in a completely darkened room, and then take a flash photo while you hold a ruler near your eyes. Then measure it from the photo. I got 7mm with a precision of better than 0.5mm last time I tried it. Note that an electronic flash this isn't the most pleasant thing to look at when you're dark adapted, but it won't kill you either.

Tom:

I have wondered about doing this. My concern is whether the image is in focus. How did you ensure that the camera was focused? Or maybe it just was???

Let's be clear - my contention is that one's pupils contract and dilate in response to the brightness of what is seen through the eyepiece, and that other chemical stuff is going on is not in dispute. I also am claiming that when folks target a certain exit pupil for observing the Moon, or Jupiter, or M42, or M13, etc. they really have no idea what will be the actual diameter of their eye's pupil as it responds to the brightness of that exit pupil. So, it seems to me that I need to determine 1) the brightness levels of the exit pupils of various targets (e.g. by using a sky meter), and 2) the response of my pupil to those brightness levels in terms of pupil diameter.

The hard part will be controlling for pupil contraction/dilation from other sources: Pavlovian conditioning, fear, **** attraction, etc. I will have to stay cool, calm and collected. Not my strong suit.

. they really have no idea what will be the actual diameter of their eye's pupil as it responds to the brightness of that exit pupil. So, it seems to me that I need to determine 1) the brightness levels of the exit pupils of various targets (e.g. by using a sky meter), and 2) the response of my pupil to those brightness levels in terms of pupil diameter.

Dennis:

First, lets eliminate Jupiter and the moon, these are bright targets and normally observed at exit pupils smaller than the diameter of the eye during the day.

Then I suggest just measuring the diameter of your dilated pupil under a variety of low light conditions. I think you will find that the dilated diameter of you pupil does not change. There is so little light from the night sky that the pupil is always at it's maximum dilate if the skies are at all dark.

I just followed Tom's suggestion and photographed my dilated eye in a closet. I waited about a minute for the immediate dark adaptation finish. The flash wouldn't work without the LCD display turned on so it was not all that dark. Under those circumstance, my pupil was very close 7mm.

Attached Files

There is so little light from the night sky that the pupil is always at it's maximum dilate if the skies are at all dark.

I do not accept that because a sky is "dark" means that all exit pupils will be (even nearly) as dark, and I know you don't either as you specifically want to treat the Moon and Jupiter as exceptions though they reside in a dark sky. However, we don't have to settle this here and now. I am going to measure the brightness of some exit pupils and post the results. Then, if the data so warrants, we can subject ourselves to further cruel but necessary experiments (I see you have already begun) to determine our pupil's responses to these levels of brightness.

One other thing I have learned is that the pupils work together - a light producing a constriction of the pupil of one eye will produce a consensual constriction of the pupil of the other eye. This further complicates my testing, as I have to be careful that my bad eye doesn't taint the results by looking at something that it oughtn't.